The present invention relates to a fuel assembly for a nuclear reactor with a detachable top tie plate to make possible reconditioning of the fuel assembly.
A fuel assembly of a known design comprises a plurality of fuel rods and guide tubes for control rods or arranged as water tubes only in certain, special nuclear reactors, the fuel rods and guide tubes being kept in predetermined mutual positions by means of spacer lattices placed along the fuel assembly. The top tie plate and the bottom tie plate at the ends of the fuel assembly are fixed to the guide tubes of the control rods, which guide tubes extend somewhat above and below the ends of the fuel rods. In this known fuel assembly the guide tubes are provided on top with a top sleeve which fits into a corresponding hole through the top tie plate. A peripheral slot is arranged in the hole, a bead around the upper part of the top sleeve fitting into this slot. The top sleeve is provided with an axial slit, extending from its upper end through the bead and made of a resilient material The slit permits the upper end of the top sleeve to be squeezed together so that the top sleeve can be moved in the hole of the top tie plate to a position in which the bead falls into the slot, whereupon the end is allowed to rebound. To ensure the locking between the top sleeve and the top tie plate, a locking sleeve is inserted into the top sleeve, which locking sleeve prevents the bead from leaving the slot. A drawback of this design is that a rather extensive machining of the top tie plate must be performed, such as, for example, milling of slots in the holes. Further, when mounting the top tie plate, all top sleeves must be squeezed together more or less simultaneously in order for the top tie plate to be fitted onto the top sleeve. Accordingly, this mounting may become quite problematic.